1. Field of the Invention
The invention relates generally to localizing wires and more particularly to a localizing wire which comprises an anchor portion having collapsible properties enabling the anchor portion to be retracted into a cannula lumen for repositioning or removal in a tissue mass. In another aspect, the invention relates to a localizing wire configured such that an externally extending portion of the wire can lie against the exterior of the tissue mass. In yet another aspect, the invention relates to a method of using the localizing wire. In one other aspect, the invention relates to a localizing wire that can be removed from a tissue mass without the re-introduction of a cannula.
2. Description of the Related Art
Localizing wires are well-known devices for marking areas, such as lesions, in a tissue mass, frequently breast tissue. When such a lesion is identified with a medical imaging technique, such as radiography or ultrasonography, it is often desirable to position a localizing wire or other type of imaging marker near the lesion to facilitate locating the lesion during later procedures, such as biopsy or surgery. Alternatively, a localizing wire, tissue marker or staple can be placed in the tissue mass after a biopsy has been performed. In the latter case, the localizing wire marks the location of the biopsy cavity for future procedures.
Localizing wires typically comprise an anchor portion implanted at the tissue site of interest, with a wire portion extending from the anchor portion to exit through the skin. A practitioner can then use the wire as a visual and tactile guide to the lesion rather than solely relying on imaging techniques, which currently provide good 2-D images but not 3-D images. During surgery, surgeons typically prefer a localizing wire to locate the lesion because it leads them straight to the biopsy site.
To implant a localizing wire, a needle, or cannula, is inserted into the tissue mass and, with guidance from an imaging system, is positioned with its tip at a selected location at or near the lesion. Once the needle is in place, the localizing wire is extended through the needle and out the tip into or adjacent the lesion where the hook on the end of the wire engages the tissue mass. Thereafter, the needle is removed from the tissue mass, and the localizing wire remains anchored in place by the hook.
It is critical that the localizing wire be accurately placed at the desired location within the tissue and remain in the desired location. Movement of the localizing wire after it is properly located and implanted is very undesirable as it will not properly identify the lesion or the biopsy site if a follow-up surgery is required.
However, there is often a need to reposition the localizing wire after the initial implantation. For a variety of reasons, such as, for example, the nature of the instrument used for implanting, the initial implantation may not always be located at the desired site. Under such circumstances, the localizing wire will need to be repositioned. Thus, a contemporary localizing wire must perform the conflicting functions of keeping the localizing wire anchored at the desired implantation site while permitting the repositioning of the localizing wire.
Prior localizing wires accomplished these conflicting functions by the anchor having a pointed, hook shape and being formed of a memory metal, such as Nitinol. When the localizing wire was stored in the cannula, the anchor was substantially straight and took on the hook shape only as it was extended exteriorly of the cannula. As the anchor was extended from the cannula, it pierced the surrounding tissue and formed the hook shape to anchor the localizing wire to the tissue. The localizing wire could be repositioned by withdrawing the anchor back into the cannula to straighten out the hook. The cannula would then be repositioned and the anchor once again extended to anchor the wire. The curvature of the hook shape was great enough that the anchor would not defect in response to an external pulling on the wire.
While the prior localizing wire adequately accomplished the conflicting functions, it does have certain known disadvantages. One such disadvantage is that the tissue is pierced each time the localizing wire is repositioned, which causes additional trauma. It is better to minimize the trauma to the surrounding tissue for reduced recovery time and the patient's comfort. Thus, there remains a need for a device that can reimplant or remove a localizing wire in a tissue mass after initial implantation with minimal discomfort to a patient.
Another disadvantage of current localizing wires is that, after implantation, a portion of the localizing wire extends exteriorly of the tissue. This exteriorly extending portion of the localizing wire projects away from the surface of the tissue mass. While the projecting of the exterior portion of the wire is useful for the surgeon in locating the localizing wire during surgery, it creates the risk that the patient or someone else might accidentally catch the exteriorly extending portion and pull or tug on the localizing wire, resulting in the possible repositioning of the localizing wire inside the tissue. Such an accidental repositioning is very undesirable in that the localizing wire will no longer properly locate the lesion and it can be painful for the patient. This is one of the reasons why localizing wires are typically inserted just prior to the surgery and are not intended to be left in the tissue mass for an extended period.
In practice, because of the several hour or several day delay between the time that a biopsy is taken and the results of the tissue analysis is received, it is a common practice for an internal imaging marker, such as that disclosed in U.S. Pat. No. 6,575,991, to be placed at the biopsy site. If the analysis of the tissue indicates that follow-up surgery is required, then a localizing wire is placed within the tissue at the site of the internal imaging marker prior to surgery and the surgeon uses the localizing wire to locate the biopsy site. It is desirable to have a localizing wire that can be used instead of the internal imaging marker to mark the biopsy site, left within the tissue for an extended period of time, and used to guide the surgeon if surgery is required or easily removed if surgery is not required.